1. Field of the Invention
The invention is related to the field of communication networks and, in particular, to transmitting text and/or multimedia messages over bearer connections that are reserved for non-voice circuit-mode data communications.
2. Statement of the Problem
A typical wireless or mobile network includes a plurality of base stations that communicate via radio frequencies to mobile devices, such as cell phones. Each base station connects to a Base Station System (BSS) which in turn connects to a Mobile Switching Center (MSC) or a similar switching office over a backhaul network. The interfaces between the MSC, the BSS, and the base stations may be based on a proprietary protocol that is defined by the vendor that manufactures the equipment. In other cases, non-proprietary interfaces may be used between the MSC, the BSS, and the base stations so that the equipment does not have to be provided by a single vendor. One example of non-proprietary interfaces is defined in the Interoperability Specification (IOS). The IOS is a standard that describes the overall system functions, including services and features required for interfacing a base station with an MSC (through a BSS), with other base stations, or with a Packet Control Function (PCF). The standard is intended to describe the interfaces used to support the interoperability of one vendor's equipment with another vendor's equipment.
The BSS and the MSC in a mobile network are connected through a signaling interface and one or more bearer interfaces. Signaling connections of the signaling interface are intended to provide a path for signaling traffic, which is used to setup and tear down calls. Bearer connections of the bearer interface are intended to provide paths for user traffic, which represents the actual voice traffic for a voice call, represents the actual data traffic for data calls, etc. As an example of signaling and bearer interfaces, the IOS standards have defined an A1 interface, which is a signaling interface that carries signaling traffic between Call Control (CC) and Mobility Management (MM) functions of the MSC and the call control component of a BSS (i.e., a Base Station Controller (BSC)). The IOS standards have also defined an A2 interface, which is a bearer interface that carries user traffic in the form of 64/56 kbps PCM information (voice/data traffic) between a switch component of the MSC and the BSS (i.e., a channel element or a Selection/Distribution Unit (SDU)). The IOS standards have further defined an A5 interface, which is an interface that carries user traffic for circuit-mode data calls (i.e., fax or modem calls) between the between the MSC and the BSS (i.e., an SDU).
In many mobile networks, text messaging and multimedia messaging has increased in popularity. Short Message Service (SMS) is a communications protocol allowing the interchange of short text messages (i.e., 160 characters) between mobile devices. Multimedia Messaging Service (MMS) is a communications protocol allowing the interchange of multimedia objects (i.e., images, audio, video, rich text) in addition to text. Often times, mobile users more frequently use text messaging and multimedia messaging for communication than voice calls.
Text/multimedia messages are presently transmitted over the signaling interface between the BSS and the MSC. For example, in a Mobile Terminated (MT) SMS message the MSC receives the SMS message from an SMS Center (SMS-C), and routes the SMS message to the BSS using a signaling interface, such as the IOS A1 interface. In a Mobile Originated (MO) SMS message, the BSS receives the SMS message generated in the mobile device, and routes the SMS message to the MSC over a signaling interface, such as the IOS A1 interface.
The increased popularity of text/multimedia messages may cause a problem on the signaling interface with voice calls. In addition to transporting text/multimedia messages, the signaling interface is also used to transport call setup messages for voice calls. A large enough amount of text/multimedia message traffic can cause congestion on the signaling interface, which results in higher call setup delays for the voice calls. Also, during call setup, the MSC sets timers indicating when a signaling message response is expected back from the BSS, and vice-versa. If the signaling interface is congested by a large amount of text/multimedia message traffic, then the signaling message responses may not be received before a time-out, which results in a dropped call. High call setup delays and dropped calls are significant to mobile service providers that are guarantying particular Quality of Service (QoS) levels.